In typical commercial reproduction apparatus (electrostatographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles (dry ink) are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the dry ink developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
In electrostatographic reproduction apparatus, the toner images can be fixed on respective receiver member by microwaves. The procedure of the microwave fusing is a volume-heating procedure and melts the toner on the front and back of the receiver member to be fixed simultaneously to both sides of the receiver member. When printing individual receiver member sheets, it is advantageous for the receiver member transport to warm up the receiver member in segments and to thus fix the toner in such segments. This is accomplished for example by arranging several microwave applicators in a staggered fashion in direction of the receiver member transport (in-track direction) as well as in the direction transverse to the transport direction of the receiver member (cross-track direction).
An overlapping range of few millimeters in width must exist between the areas warmed up by the individual applicators due to the heating profiles in the individual applicators transverse to the transportation direction. The image quality within the overlapping range is unfavorably affected, if the receiver member and the toner on such receiver member cool down too much between the warming up steps. Thus the gloss and possibly the density of the print image will be different within the overlapping range in comparison to the remaining print area, due to the fact that the toner warms up in only one applicator and cools down afterwards. In order to avoid this warm up/cool down phenomena, cooling of the receiver member within the overlapping range, below a critical temperature, must be avoided. Devices based on IR or UV radiation, or on hot air have the disadvantage that they cannot easily and precisely be restricted to heating in the overlapping range, which can lead to further negative influences on the image quality.